It has long been recognized that halogen-containing organic polymers, particularly the commercially important polyvinyl chloride polymers, are subject to deterioration or degradation when exposed to the deleterious effects of heat, light and weathering. Various compounds and compositions have been advanced to stabilize these polymers against such deterioration and degradation. For the most part, these stabilizers have been primarily directed toward stabilization against the effects of heat, such as that encountered during processing of the polymer and fabrication into articles. Among these heat stabilizers some of the most effective have been a wide variety of organotin compounds.
For example, organotin oxides and sulfides were suggested by U.S. Pat. No. 2,267,777 Yngve, U.S. Pat. No. 2,746,946 to Weinberg and U.S. Pat. No. 3,021,302 to Frey as heat stabilizers for polyvinyl chloride. However, these compounds are not really very effective heat stabilizers and have never achieved any commercial success.
Numerous patents, such as Kauder et al U.S. Pat. No. 3,817,915, Leistner U.S. Pat. No. 2,641,588 and Brecker et al U.S. Pat. No. 3,640,953 disclose organotin mercaptides and diorganotin mercaptocarboxylic acid esters combined with a diorganotin oxide-ester complex as heat stabilizers for vinyl halide polymers and these have now been generally recognized as among the most effective for inhibiting degradation of polyvinyl chlorides at high temperatures of up to 350.degree. or 375.degree. F. to which they are subjected during processing. However, these mercaptides produce objectionable odors and the polymer often retains some of this odor in the finished product. Moreover, these organotin mercaptide compounds are not effective stabilizers against light and weathering and, in fact, suffer from poor weatherability. It is generally necessary to include more than 10% titanium dioxide pigment in the formulation in an attempt to improve UV resistance. Yet, this is highly undesirable, especially for dark pigmented products.
In U.S. Pat. Nos. 2,597,920 to Caldwell and 2,763,632 to Johnson, it is suggested that reaction products of diorganotin oxides and esters of oxygen-containing acids may be utilized as heat and light stabilizers for polyvinyl chloride resins. However, these reaction products are also rather poor in stabilizing effectiveness and have not been adopted for widespread use.
It has also been suggested in various patents, such as U.S. Pat. No. 2,938,013 to Mack et al and U.S. Pat. No. 2,307,157 to Quattlebaum et al, to employ organotin carboxylates having tetravalent tin atoms which have one or two direct tin to carbon bonds and the remainder of the bonds on the tin being tin to oxygen to carbonyl bonds. While these compounds have been found to be somewhat effective, UV light stabilizers for polyvinyl halide resins are poor heat stabilizers. Moreover, these stabilizers suffer from the drawback that they are primary irritants to the eyes and mucous membranes and the fumes generated during the processing of polyvinyl halide stabilized therewith are lachrymatory. Furthermore, these organotin carboxylates are incompatible with normally used microingredients such as calcium stearate, employed during processing of polyvinyl halide formulations.
A stabilizer composition of an organotin maleate and a maleate ester are disclosed as heat stabilizers for halogen-containing organic polymers in U.S. Pat. No. 3,379,679 but these do not provide adequate heat stability. In addition, such combination is also incompatible with normally used microingredients, employed in commercial polymer formulations, and can cause problems with eye irritation and offensive odors due to the presence of the organotin maleate. Thus, the industry has not been able to use organotin maleates as light stabilizers because of the aforementioned problems.
Yet, with the increasing use of halogen-containing organic polymers for rigid articles which will be exposed to light and outdoor weathering for extended periods of time, such as housing siding and window profiles, it has become increasingly important to develop a stabilizer which will not only protect the polymer against the high temperatures and heat encountered during processing and fabrication but will also protect the polymer against the extended and long-term effect of light and weathering as well.
It is, therefore, highly desirable that a stabilizing composition be provided for halogen-containing organic polymers which is effective as a stabilizer against heat, light and weathering as well as not exhibiting eye and mucous membranes irritation. It is also desirable to provide such a stabilizing composition which provides excellent heat stability for polyvinyl chloride resins rivaling that obtained with organotin mercaptides, while obtaining excellent light and weathering stability similar to that obtained with organotin carboxylates. It would also be highly advantageous to obtain such heat, light and weathering stability while permitting a reduction in the level of titanium dioxide pigment levels to about 3 to 6% or less.